1. Field of the Invention
The present invention relates to the separation of monoepoxides such as propylene oxide from oxygenated impurities by extractive distillation with a lower glycol while avoiding substantial conversion of the monoepoxide.
2. Description of the Prior Art
Monoepoxides such as propylene oxide are highly important chemicals useful in a great number of applications. An important commercial technology for producing the monoepoxides is via the catalytic reaction between the corresponding olefin and an organic hydroperoxide. See, for example, U.S. Pat. No. 3,351,635.
In carrying out this reaction the organic hydroperoxide is reduced to the corresponding alcohol. Also produced, however, are small amounts of other oxygen-containing compounds such as methanol, acetone, acetaldehyde and the like. In general, the alcohol resulting from the reduction of the hydroperoxide can be separated from the epoxide product by ordinary distillation methods, particularly since the organic hydroperoxide employed can be selected to permit this separation. The small amounts of the other oxygenated compounds, however, remain as impurities in the olefin oxide product. For certain of the epoxides, it is extremely important that these impurities be reduced to the low p.p.m. level.
It has previously been proposed to separate these oxygencontaining impurities from the monoepoxide by extractive distillation using lower glycols such as ethylene glycol and propylene glycol. See U.S. Pat. No. 3,578,568 which describes this procedure and which teaches use of solvent in amount to comprise 15 to 50% of the vapor space in the distillation zone. While this previously described separation is quite effective to produce the desired high purity monoepoxide, the methods described result in the loss of small but significant amounts of the valuable monoepoxide by virtue of the reaction between the glycol distillation solvent and the monoepoxide to be purified.